1. Field of Invention
This invention is a pump for delivering fuel to an internal combustion engine in which engine pressure, preferably cylinder pressure, acts on and moves a piston whose displacement is affected by two opposed regulating springs. These regulating springs affect the pump""s specific fuel output, its fuel output divided by the engine cylinder""s peak pressure, for various engine torque levels. The spring rate and pre-load of these springs provide tuning adjustments to the pump. The use of these springs allows construction of a totally mechanical fuel injection pump requiring no electrical components in its operation.
2. Description of Prior Art
Various mechanical or partially mechanical fuel injection systems have been developed, and engine cylinder or crankcase pressure has been used to control various functions of these systems. Totally mechanical systems, though desirable from the standpoint of simplicity, have not gained wide usage due to a difficulty in precisely shaping fuel flow as a function of engine load. Electrical systems or hybrid electrical/mechanical systems have been developed to overcome this problem.
U.S. patents to O""Neill, U.S. Pat. No. 4,098,560 (1978) and U.S. Pat. No. 4,141,675 (1979), describe a fuel pump driven by cylinder pressure. The fuel metering is performed by an electronic xe2x80x9cinterface control unitxe2x80x9d, and the pump, driven by cylinder pressure, is designed to provide a constant fuel pressure at the injection nozzles. The pump has two pistons acted on by a xe2x80x9csingle springxe2x80x9d, and a xe2x80x9climit is placed on the piston""s upward strokexe2x80x9d (U.S. Pat. No. 4,141,675). This causes the fuel pressure from the pump to equal the pressure exerted on the fuel by the spring when the piston has reached its stop. This constant pressure is the main concern of the pump of these patents, as stated in U.S. Pat. No. 4,141,675; xe2x80x9cAlso, since engine combustion pressures vary with operating conditions and deterioration is practically unavoidable it is important that the gas-driven pump be designed so that the fuel pressure does not changexe2x80x9d. This pump is therefore not used to regulate the flow of fuel to the engine, the regulation again being performed electronically.
U.S. Pat. No. 5,494,015 to Rynhart (1996) discloses a fuel injector assembly which uses cylinder pressure to operate a xe2x80x9csnap actionxe2x80x9d piston which times the fuel (and air) injection event. Cylinder pressure is applied to a small diameter of the piston which becomes initially slightly unseated exposing a larger area of the piston to cylinder pressure. This causes the piston to xe2x80x9csnapxe2x80x9d open, allowing the fuel injection event to occur. There is a limiting shoulder, however, on the piston body which limits the piston movement and seals the fuel injector from combustion gases. The piston always has a fixed displacement, moving between two limit positions. The amount of fuel injected is not determined by the piston""s movement but is determined by changing the relative orientation of two spill ports, thus changing the effective stroke of the fuel injector plunger. In U.S. Pat. No. 4,048,970 to Fitzgerald (1977), a shuttle valve is operated by cylinder pressure between two limit positions, thus timing the injection event. Oil under pressure is used to provide the force for the fuel injection process, the pressure of this oil being regulated by a spool valve. This spool valve is positioned by a mechanical actuating rod, and the position of this actuating rod therefore determines the amount of fuel injected. In both of these patents, cylinder pressure is used to time the fuel injection event but does not regulate the quantity of fuel injected. U.S. patents to May, U.S. Pat. No. 3,425,403 (1969) and U.S. Pat. No. 3,805,758 (1974), describe a totally mechanical fuel injection pump which is designed to be a pumping and fuel regulating means. This pump is driven by crankcase or cylinder pressure applied to a resilient membrane, and the pumping action is obtained by the action of suitable inlet and outlet valves, known in the art. The membrane is in effect a single spring, and this single spring affects fuel delivery at all engine loads.
Applicant""s co-pending application Ser. No. 09/550,774 describes a fuel injection pumps which have a moveable partition between an engine pressure chamber and a fuel chamber. This moveable partition is shown as a combination of a diaphragm and a piston and its movement is affected by the xe2x80x9cspringxe2x80x9d of an o-ring and the xe2x80x9cspringxe2x80x9d contained in the flexibility of the diaphragm. Both of these xe2x80x9cspringsxe2x80x9d affect the movement of the diaphragm and piston at all engine torque levels.
It is an object of this invention to provide a fuel injection pump driven by engine pressure, preferably from the engine cylinder, acting on a piston the movement of which is affected by two opposed springs. These opposed springs are pre-loaded, or compressed, such that both springs affect piston movement at small piston displacements, but only one spring affects piston movement at greater piston displacements. The spring rates of these two springs can be selected and their pre-load adjusted to affect the specific fuel output of the pumps at different engine torque levels. This allows the construction of a totally mechanical fuel injection system, requiring no electrical components.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.